In the use of liquids and solid materials as source reagents for vapor in CVD, ALD and ion implantation, various reagents materials are employed. The reagent materials may be heated to form source reagent vapor that is delivered to process equipment for deposition or implantation. To achieve successful CVD, ALD, and ion implantation, the source reagent vapor should be supplied at a consistent, controlled, and reproducible rate.
In producing reagent vapor, such as for single wafer deposition or implantation, it is important to uniformly heat the source reagent material. There may be significant differences in boiling points and sublimation temperatures of source reagents to be vaporized. If the source reagent material is not heated uniformly, cold spots or hot spots may exist among units of the source reagent material, and such non-uniform heating may result in fluctuations in the reagent vapor flow. It is also desirable to circulate carrier gas among the source reagent material and the reagent vapor generated to mix the carrier gas and the source reagent vapor generated by the source reagent material.
Solid source reagents are particularly difficult to control in volatilization applications where sublimation temperatures are close to temperatures at which thermal disassociation occurs and yields thermal degradation by-products that are detrimental to the downstream deposition or ion implantation process. Solid source delivery also can be complicated by surface morphology of the solid source reagent changing during volatilization and depletion of the solid source material during volatilization, both of which may result in a change in the surface area of the solid source material that is exposed to the carrier gas.
Producing reagent vapor for deposition or implantation of batches of multiple wafers poses further problems. Deposition or implantation of batches of wafers may necessitate a greater flow of reagent vapor. A greater flow of vapor may require heating of large batches of source reagent material that, in turn, may require use of a larger vaporizer vessel and larger support structures to accommodate the source reagent material. Using a larger quantity of source reagent material in a larger vaporizer vessel may make it more difficult to consistently engage a carrier gas with the source reagent material and reagent vapor generated by the source reagent material to efficiently entrain the reagent vapor in the resulting gas mixture. Further, uniform heating of larger batches of source reagent material may be more difficult than uniformly heating small batches of source reagent material. Producing greater quantities of reagent vapor also may necessitate replacing batches of source reagent material more frequently, so it may be desirable to simplify the task of reloading the source reagent material in the heating apparatus.
At the same time, concerns related to preventing non-vaporous particles from passing into the reagent vapor flow for a relatively small flow of reagent vapor may be magnified when generating a larger flow of reagent vapor. Heating larger quantities of source reagent materials may result in production of greater quantities of particles as a result of thermal decomposition during heating. Flows of reagent vapors may be filtered to prevent these unwanted particles from being introduced into the deposition or implantation process. However, filtering out particles from a larger flow of reagent vapor, such as may be used for batch deposition or implantation, may be more complex than filtering a lesser flow of reagent vapor.